**Pedro F. Mayuet Ares \*, Juan Manuel Vázquez Martínez, Mariano Marcos Bárcena and Antonio J. Gámez**

Department of Mechanical Engineering & Industrial Design, Faculty of Engineering, University of Cadiz, Av. Universidad de Cádiz 10, E-11519 Puerto Real (Cadiz), Spain; juanmanuel.vazquez@uca.es (J.M.V.M.); mariano.marcos@uca.es (M.M.B.); antoniojuan.gamez@uca.es (A.J.G.) **\*** Correspondence: pedro.mayuet@uca.es; Tel.: +34-616-852-858

Received: 1 July 2018; Accepted: 13 August 2018; Published: 18 August 2018

**Abstract:** Plastic matrix composite materials are an excellent choice for structural applications where high strength-weight and stiffness-weight ratios are required. These materials are being increasingly used in diverse industrial sectors, particularly in aerospace. Due to the strict tolerances required, they are usually machined with drilling cycles due to the type of mounting through rivets. In this sense, laser beam drilling is presented as an alternative to conventional drilling due to the absence of tool wear, cutting forces, or vibrations during the cutting process. However, the process carries with it other problems that compromise the integrity of the material. One of these is caused by the high temperatures generated during the interaction between the laser and the material. In this work, variance analysis is used to study the influence of scanning speed and frequency on macro geometric parameters, surface quality, and defects (taper and heat affected zone). Also, in order to identify problems in the wall of the drill, stereoscopic optical microscopy (SOM) and scanning electron microscopy (SEM) techniques are used. This experimental procedure reveals the conditions that minimize deviations, defects, and damage in machining holes.

**Keywords:** laser beam machining; carbon fiber reinforced polymer; hole quality characteristics; geometrical parameters; roughness parameters; taper; heat affected zone
